High aperture LCD with insulating color filters overlapping bus lines on active substrate

ABSTRACT

A high aperture active matrix liquid crystal display (AMLCD) includes pixel electrodes in respective pixels which overlap adjacent address lines. The color filters are formed on the active substrate in a manner such that the filters also overlap the address lines and function as an insulating layer between the pixel electrodes and address lines in the areas of overlap. Accordingly, line-pixel capacitances are reduced and the resulting AMLCD is easier to manufacture. The total number of process step in manufacturing is reduced, and plate-to-plate (active to passive plate) alignment is much easier and less important.

This application is a continuation of application Ser. No. 09/356,302filed Jul. 16, 1999, now U.S. Pat. No. 6,365,916, which is acontinuation of Ser. No. 08/908,803 filed Aug. 8, 1997, now U.S. Pat.No. 5,994,721, which is a continuation-in-part application of Ser. No.08/671,376 filed Jun. 27, 1996, now U.S. Pat. No. 6,376,270, which is acontinuation-in-part application of Ser. No. 08/630,984 filed Apr. 12,1996, now U.S. Pat. No. 6,372,534, which in a continuation-in-art ofapplication Ser. No. 08/470,271, filed Jun. 6, 1995, now abandoned.Also, this application is related to commonly owned U.S. Pat. No.5,641,974, and Ser. No. 08/832,345, the disclosures of which areincorporated herein by reference.

This invention relates to a liquid crystal display (LCD) having anincreased pixel aperture ratio and different colored polymer filters.More particularly, this invention relates to a liquid crystal displayincluding an array of TFTs wherein photo-imageable color filters havingcontact vias or apertures disposed therein are located on the activesubstrate between the address lines and pixel electrodes so that thepixel electrodes and color filters may both be permitted to overlap atleast one of the row and column address lines without exposing thesystem to capacitive cross-talk, thereby providing an efficient andcommercially improved high aperture LCD.

BACKGROUND OF THE INVENTION

Electronic matrix arrays find considerable application in X-ray imagesensors and active matrix liquid crystal displays (AMLCDs). Such AMLCDsgenerally include X and Y (or row and column) address lines which arehorizontally and vertically spaced apart and cross at an angle to oneanother thereby forming a plurality of crossover points. Associated witheach crossover point is an element (e.g. pixel) to be selectivelyaddressed. These elements in many instances are liquid crystal displaypixels or alternatively the memory cells or pixels of an electronicallyadjustable memory array or X-ray sensor array.

Typically, a switching or isolation device such as a diode or thin-filmtransistor (TFT) is associated with each array element or pixel. Theisolation devices permit the individual pixels to be selectivelyaddressed by the application of suitable potentials between respectivepairs of the X and Y address lines. Thus, the TFTs act as switchingelements for energizing or otherwise addressing corresponding pixelelectrodes.

Amorphous silicon (a-Si) TFTs have found wide usage for isolationdevices in liquid crystal display (LCD) arrays. Structurally, TFTsgenerally include substantially co-planar source and drain electrodes, athin-film semiconductor material (e.g. a-Si) disposed between the sourceand drain electrodes, and a gate electrode in proximity to thesemiconductor but electrically insulated therefrom by a gate insulator.Current flow through the TFT between the source and drain is controlledby the application of voltage to the gate electrode. The voltage to thegate electrode produces an electric field which accumulates a chargedregion near the semiconductor-gate insulator interface. This chargedregion forms a current conducting channel in the semiconductor throughwhich current is conducted. Thus, by controlling the voltage to the gateand drain electrodes, the pixels of an AMLCD may be switched on and offin a known manner.

Typically, pixel aperture ratios (i.e. pixel openings) innon-overlapping AMLCDs are only about 50% or less. As a result, eitherdisplay luminance is limited or backlight power consumption isexcessive, thereby precluding or limiting use in certain applications.Thus, it is known in the art that it is desirable to increase the pixelaperture ratio or pixel opening size of LCDs to as high a value aspossible so as to circumvent these problems. The higher the pixelaperture ratio (or pixel opening size) of a display, for example, thehigher the display transmission. Thus, by increasing the pixel apertureratio of a display, transmission may be increased using the samebacklight power, or alternatively, the backlight power consumption maybe reduced while maintaining the same display luminance.

It is known to overlap pixel electrodes over address lines in order toincrease the pixel aperture ratio. For example, “High-Aperture TFT ArrayStructures” by K. Suzuki discusses an LCD having an ITO shield planeconfiguration having a pixel aperture ratio of 40% and pixel electrodeswhich overlap signal bus lines. An ITO pattern in Suzuki located betweenthe pixel electrodes and the signal lines functions as a ground plane soas to reduce coupling capacitance between the signal lines and the pixelelectrode. Unfortunately, it is not always desirable to have a shieldelectrode disposed along the length of the signal lines as in Suzuki dueto production and cost considerations. The disposition of the shieldlayer as described by Suzuki requires extra processing steps and thuspresents yield problems. Accordingly, there exists a need in the art fora color LCD with an increased pixel aperture ratio which does notrequire an ITO shield plane structure to be disposed between the signallines and pixel electrode.

It is old and well-known to make TFT arrays for LCDs wherein addresslines and overlapping pixel electrodes are insulated from one another byan insulating layer. For example, see U.S. Pat. Nos. 5,055,899;5,182,620; 5,414,547; 5,426,523; 5,446,562; 5,453,857; and 5,457,553.

U.S. Pat. No. 5,182,620 discloses an AMLCD including pixel electrodeswhich at least partially overlay the address lines and additionalcapacitor lines thereby achieving a larger numerical aperture for thedisplay. The pixel electrodes are insulated from the address lines whichthey overlap by an insulating layer formed of silicon oxide or siliconnitride. Unfortunately, the method of making this display as well as theresulting structure are less than desirable because: (i) chemical vapordeposition (CVD) is required to deposit the silicon oxide or siliconnitride insulating film; (ii) silicon oxide and silicon nitride are notphoto-imageable (i.e. contact holes or vias must be formed in suchinsulating layers by way of etching); and/or (iii) the dielectricconstants of these materials are too high and thereby render the LCDsusceptible to cross-talk problems. Still further, the '620 patent doesnot discuss or contemplate color filter issues. As a result of theseproblems, the manufacturing process is both expensive and requires moresteps than would be otherwise desirable. For example, in order to etchthe contact holes in an insulating layer, an additional photoresistcoating step is required and the user must be concerned about layersunderneath the insulating layer during etching. With respect to CVD,this is a deposition process requiring expensive equipment. Furthermore,if the color filters are on the passive substrate, as they typicallyare, alignment of the active and passive plates is difficult andrequires expensive equipment and expertise.

In the prior art, color filters in active matrix liquid crystal displays(AMLCDs) are typically located on the substrate (the passive plate orsubstrate) which opposes the active matrix substrate. In other words,the color filters and TFTs (or diodes) are typically located ondifferent substrates, on opposite sides of the liquid crystal (LC) layer[e.g. see U.S. Pat. No. 5,499,126]. Black matrix formation is alsotypically provided on the color filter substrate. The provisions of theblack matrix and color filters on the substrate opposite the activematrix is, of course, costly, time consuming, and requires numerousmanufacturing steps. As discussed above, this also requires difficultand time consuming alignment steps.

The LCD structure disclosed in U.S. Pat. No. 5,641,974 utilizes atransparent polymer insulating layer on the active substrate to provideisolation between address lines and overlapping pixel electrodes. Whilethis design work well and achieves superior results, it unfortunately,in practice, requires each of: (i) providing the transparent polymerinsulating layer on the active substrate; (ii) providing color filterson the opposite substrate; (iii) providing a black matrix on the colorfilter substrate; (iv) very accurate plate-to-plate (i.e.substrate-to-substrate) alignment; and (v) the process steps requiredfor (ii)-(iv) above.

It is apparent from the above that there exists a need in the art for animproved high aperture AMLCD design, and method of manufacturing same,which (i) reduces the number of total manufacturing process stepsrequired; (ii) eliminates the need for the combination of (a) theoptically transparent insulating layer sandwiched between the addresslines and pixel electrodes, and (b) the color filters; (iii) reduces theneed for the black matrix on the substrate opposite the activesubstrate; (iv) provides for a high pixel aperture ratio; and/or (v)reduces the accuracy required in plate-to-plate alignment (i.e.eliminates the need for sophisticated alignment machines).

It is a purpose of this invention to fulfill the above-described needsin the art, as well as other needs which will become apparent to theskilled artisan from the following detailed description of thisinvention.

SUMMARY OF THE INVENTION

Generally speaking, this invention fulfills the above-described needs inthe art by providing a high aperture color LCD including color filters,the display comprising:

first and second substrates;

a liquid crystal layer sandwiched between the first and secondsubstrates;

first and second different colored pixels, said first pixel including onsaid first substrate a first pixel electrode, a first insulating colorfilter, and a first thin film transistor (TFT), and said second pixelincluding on the first substrate a second pixel electrode, a secondinsulating color filter, and a second TFT, wherein said first and secondcolor filters are differently colored;

the first and second pixel electrodes overlapping with correspondingaddress lines in communication with TFTs so as to define a high aperturedisplay, the overlapping forming areas of overlap;

the first insulating color filter being at least partially disposed inan area of overlap in the first pixel, the first color filter having adielectric constant of less than about 5.0 and having a first contacthole defined therein that allows the first pixel electrode to beelectrically connected to the first TFT; and

said second insulating color filter being at least partially disposed inan area of overlap in the second pixel, the second color filter having adielectric constant less than about 5.0 and having a second contact holedefined therein that allows the second pixel electrode to beelectrically connected to the second TFT.

In certain embodiments, each of the first and second color filters areof a photo-imageable material that includes a color dye or pigment.

In certain embodiments, the LCD includes arrays of only two coloredpixels, while in other embodiments the display may include arrays ofthree differently colored pixels, or four differently colored pixels.

Surprisingly, it has been found that the thickness of the metal pixelelectrode layers (e.g. ITO) should be from about 300 Å-900 Å(preferablyabout 600 Å) in this invention in order to reduce the interface stressbetween the pixel electrodes (e.g. ITO) and the color filters.

This invention further fulfills the above-described needs in the art byproviding a method of making a color LCD having insulating colorfilters, the method comprising the steps of:

providing first and second substrates;

providing a liquid crystal material;

forming an array of isolation switching elements on the first substrateand a plurality of address lines in communication with the isolationswitching elements;

depositing a first resist color filter layer on the first substrate overtop of the address lines and the switching elements;

photo-imaging the first resist color filter layer so as to pattern itinto a first array on the first substrate so that color filters in thefirst array are of a first color and overlap at least a portion of atleast one address line;

depositing a second resist color filter layer of a second color over topof the first array of color filters;

photo-imaging the second resist color filter layer so as to pattern itinto a second array so that color filters in the second array overlap atleast a portion of at least one address line;

forming contact holes in color filters in each of the first and secondarrays;

depositing a conductive pixel electrode layer over top of the first andsecond arrays of color filters; and

patterning the electrode layer so as to form an array of substantiallytransparent pixel electrodes wherein pixel electrodes in the arrayoverlap address lines which are also overlapped by color filters so thatthe color filters act as insulators between the pixel electrodes and theaddress lines in the areas of overlap, wherein each of the pixelelectrodes is in electrical communication with a corresponding switchingelement through one of the contact holes.

In certain preferred embodiments, each of the color filters has adielectric constant less than or equal to about 4.0 so as to reducecross-talk and coupling capacitance in the areas of overlap.

This invention will now be described with reference to certainembodiments thereof as illustrated in the following drawings.

IN THE DRAWINGS

FIG. 1 is a top view of an AMLCD active plate according to oneembodiment of this invention, this figure illustrating a plurality ofdifferent colored pixels wherein the illustrated pixel electrodes 3 andcorresponding color filters 101-104 are overlapping surrounding andproximate row and column address lines along their respective lengthsthroughout the pixel area so as to increase the pixel aperture ratio ofthe display.

FIG. 2 is a top view of the column or drain address lines andcorresponding drain electrodes of the AMLCD of FIG. 1, this figure alsoillustrating the TFT source electrodes disposed adjacent the drainelectrodes so as to define the respective TFT channels.

FIG. 3 is a top view of the pixel electrodes of FIG. 1 and thecorresponding insulating color filters, except for electrode extensions.

FIG. 4 is a side elevational cross-sectional view of a linear shaped TFTand corresponding color filter and pixel electrode of FIGS. 1-3.

FIG. 5 is a side elevational cross-sectional view of the AMLCD of FIGS.1 and 4, except that this figure does not illustrate the insulatingcolor filters or TFTs.

FIG. 6(a) is a top view of an AMLCD active plate according to anotherembodiment of this invention.

FIG. 6(b) is a side cross-sectional view of the FIG. 6(a) AMLCD, alongA—A.

FIG. 6(c) is a side cross-sectional view of a portion of the displayaccording to the FIG. 6(a) along B—B, this embodiment illustrating thecolor filters and pixel electrodes overlapping respective address linesand TFTs on the active matrix plate, this embodiment differing from thepreviously illustrated FIG. 1 embodiment in that the gate electrode inthis embodiment protrudes at a 90° angle from the gate line so as to beparallel to the drain line, in each pixel.

FIGS. 7-10 are side elevational cross-sectional views illustrating howthe active matrix in the display of FIG. 1 is manufactured according toan embodiment of this invention.

FIG. 11 is a top view of an array of colored pixels, illustrating thearray of color filter strips extending across the viewing area accordingto the FIG. 6 embodiment.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THIS INVENTION

Referring now more particularly to the accompanying drawings in whichlike reference numerals indicate like parts throughout the severalviews.

FIG. 1 is a top view of four different colored pixels (red, green, blue,and white) in an array on the active plate of an active matrix liquidcrystal display (AMLCD) 2 according to an embodiment of this invention.This particular portion of the display includes an array pixelelectrodes 3, drain address lines 5, gate address lines 7, an array offour thin-film transistors (TFTs) 9, auxiliary storage capacitors 11,and finally insulating color filters 101-103 (the peripheries of thesecolor filters are illustrated in broken or dotted lines) and optionalsubstantially clear polymer layer 104. The color layer 104 defines whitepixel (s). Each storage capacitor 11 is defined on one side by a gateline 7 and on the other side by an independent storage capacitorelectrode 12. Storage capacitor electrodes 12 are formed along withdrain electrodes 13.

For example, the number of total process steps on the active and passiveplates is reduced, and the active to passive plate alignment is mucheasier and less important. In some embodiments, up to three or morephoto steps in manufacturing can be eliminated.

As shown, the longitudinally extending edges of each pixel electrode 3and each color filter 101-103 at least partially overlap both drainlines 5 and gate lines 7, respectively, along edges thereof so as toincrease the pixel aperture ratio (or pixel opening size) of the colorAMLCD. The optically clear layer 104 in each white pixel also overlapsthe address lines. Optionally, only one of the gate lines and drainlines may be at least partially overlapped by the pixel electrode andcolor filter of a given pixel.

The red, green, and blue pixels are provided with color filters 101-103,respectively, while the white pixel may or may not be provided withclear layer 104.

The areas of overlap between the address lines (e.g. gate and/or drain)and the overlapping pixel electrodes and color filters are referred toas overlap areas 18. In each of these areas 18 of overlap between the(i) address line(s) 5, 7, and (ii) pixel electrodes 3 and color filters101-103 (and insulating layer 104), a pixel-line (PL) capacitor isdefined by an electrode 3 on one side and the overlapped conductiveaddress line 5, 7 on the other side. The dielectric disposed between theopposing electrodes of these PL capacitors is represented by theinsulating color filters 101-103 (e.g. see FIGS. 4 and 6) in the coloredpixels and layer 104 in white pixels. The parasitic capacitance C_(PL)of these capacitors is defined by the known equation:$C_{PL} = \frac{\varepsilon \cdot \varepsilon_{0} \cdot A}{d}$

where “d” is the thickness of the color filter layer, ∈ is thedielectric constant of the color filter, ∈₀ is the constant 8.85×10⁻¹⁴F/cm (permitivity in vacuum), and “A” is the area of the PL capacitor inthe overlap area 18 at issue. The fringing capacitance may also be takeninto consideration in a known manner. Also, according to certain otherembodiments, the color filters 101-103, and layer 104, are of a materialand thickness so that C_(PL) is less than or equal to about 0.01 pF fora display with a pixel pitch reference of about 150 μm. When the pixelpitch is smaller than this reference of 150 μm, C_(PL) should be scaledto a lower value as well because overlap area(s) 18 are smaller.Additionally, the pixel aperture ratio of the LCD decreases as the pixelpitch decreases, as is known in the art. The pixel pitch of AMLCD 2 maybe from about 40 to 5,000 μm according to certain embodiments of thisinvention. The pixel pitch, as known in the art, is the distance betweencenters of adjacent pixels in the array.

An important aspect of this invention is the fact that, as illustratedin FIG. 1, the color filters 101-103 (and layer 104) are provided on theactive matrix substrate (i.e. on the active plate), and act asinsulators in these capacitors between overlapping pixel electrodes 3and address lines. Accordingly, the color filters 101-103 and layer 104are patterned on the active plate so that they also overlap thecorresponding address lines so as to insulate them from the overlappingpixel electrodes 3. The color filters 101-103 and layer 104 arepatterned on the active plate so that different color filters are spacedfrom one another, between adjacent pixels, by from about 0.5 to 2.0 μmin certain embodiments. Thus, a gap “P” or space of this width isprovided over address lines between pixels, the gap “P” defined as thedistance between filters. This design simplifies the manufacturingprocess for forming the AMLCDs, and results in a more efficient displayand method of manufacture.

As illustrated in FIG. 1, color filter 101 is a red color filter, colorfilter 102 is a green color filter, color filter 103 is a blue colorfilter, and layer 104 is a substantially clear material as in U.S. Pat.No. 5,641,974). Each of color filters 101-103 is of a photo-imageablematerial, with a respective color filter pigment added thereto. Layer104 may also be photoimageable. The colors of the respective filters101-103 need not be limited to these particular colors, but may alsoassume different colors in alternative embodiments of this invention, asis known in the art. Alternatively, non-photo-imageable material may beused, with pigment or dye, as the color filters 101-103 and layer 104.

FIG. 2 is a top view of drain address lines 5 of the FIG. 1 AMLCD 2illustrating how extensions of address lines 5 form drain electrodes 13of TFTs 9. Each TFT 9 in the array includes source electrode 15, drainelectrode 13, and corresponding gate electrode 17. Gate electrode 17 ofeach TFT 9 is formed by the corresponding gate address line 7 adjacentthe TFT according to certain embodiments of this invention. In otherembodiments (e.g. see FIG. 6), gate electrode 17 for each TFT may beformed by a branch extending substantially perpendicular to the gateaddress line. Herein, a source electrode is defined as the TFT electrodethat is in communication with the pixel electrode.

FIG. 3 is a top view illustrating pixel electrodes 3 in solid lines(absent their extension portions 38) and the corresponding color filters101-103 in broken lines. FIGS. 2-3 are provided so that FIG. 1 maybemore easily interpreted. As shown in FIG. 3, the exterior periphery ofeach color filter 101-103 extends beyond the outer periphery of thecorresponding pixel electrode 3, so that each color filter 101-103 (andlayer 104) defines a greater surface area than the corresponding pixelelectrode 3. As a result of this difference in surface area, the layers101-104 act as superior insulators, each with a thickness of from about1.0-3.0 μm in the areas 18 of overlap between the pixel electrodes andthe corresponding address lines, so as to reduce cross-talk and thecoupling capacitance between the pixel electrodes 3 and overlappedaddress line(s) in the high aperture LCD.

FIG. 4 is a side elevational cross-sectional view of a single TFT 9 (ina red pixel) in the TFT array of the FIG. 1 AMLCD 2, with each TFT 9 inthe array being substantially the same as the one shown in FIG. 4according to certain embodiments. Each TFT 9 has a channel length “L”defined by the gap 27 between source electrode 15 and drain electrode13. Source electrode 15 is connected to pixel electrode 3 by way of viaor contact hole 35 defined in red color filter 101 so as to permit TFT 9to act as an isolating switching element and selectively energize acorresponding pixel/pixel electrode in AMLCD 2 in order to provide redimage data to a viewer. An array of TFTs 9 is provided as illustrated inFIG. 1 for the AMLCD, with the color filters being different colors indifferent color pixels. Alternatively, diodes may be used as isolatingswitching elements instead of TFTs.

Each TFT 9 structure includes substantially transparent active substrate19 (e.g. made of glass), metal gate electrode 17, gate insulating layeror film 21, semiconductor layer 23 (e.g. intrinsic amorphous silicon),doped semiconductor contact layer 25, drain electrode 13, sourceelectrode 15, insulating color filter or layer 101, 102, 103, or 104,and a corresponding pixel electrode 3. TFT channel 27 of length “L” isdefined between source 15 and drain 13.

Because the color filters (and layer 104) are patterned in differentcolored arrays on the active plate, the filters, as shown in FIG. 4, donot entirely overlap the whole drain electrode 13, but instead onlyoverlap a substantial portion (e.g. greater than about 25% of the drainelectrode) thereof along with the TFT channel 27 so as to insulate themfrom electrode 3 that also does not overlap the entire drain electrode.As shown in FIG. 4, the pixel electrode 3 in each pixel does not evenoverlap the drain electrode in this embodiment, although it may in someembodiments. Optionally, in certain embodiments, the filters 101-103,and layer 104, may overlap the entire TFT structure in each pixel.

If the TFT structure illustrated in FIG. 4 was for the red pixelillustrated in FIG. 1, then the insulating layer 101 between the pixelelectrode 3 and the TFT and address lines would be red insulating colorfilter 101. Likewise, if the TFT structure illustrated in FIG. 4 was forthe green pixel of FIG. 1, then the insulating layer would berepresented by color filter 102, and if the TFT structure was for theblue pixel, then the insulating layer would be represented by blue colorfilter 103. If FIG. 4 was for a white pixel, the insulating layer 104would be clear. It is pointed out that the color filters 101, 102, 103,(and layer 104) cover the channel 27 of the TFT, but only partiallycover or overlap the corresponding drain electrode 13, 29 in certainembodiments.

As illustrated in FIG. 4, drain electrode 13 is made up of drain metallayer 29 (e.g. Mo) which is deposited on active substrate 19 over top ofdoped contact layer 25. Contact film or layer 25 may be, for example,amorphous silicon doped with an impurity such as phosphorous (i.e.n+a-Si) and is sandwiched between semiconductor layer 23 and drain metallayer 29. Source electrode 15 includes doped semiconductor contact layer25 and source metal layer 31. Metal layers 29 and 31 may be of the samemetal and deposited and patterned together according to certainembodiments of this invention. Alternatively, layer 29 may be depositedand patterned separately from layer 31 so that drain metal layer is ofone metal (e.g. Mo) and source metal layer 31 is of another metal (e.g.Cr) across the array.

FIGS. 6(a), 6(b), 6(c), and 11 illustrate AMLCD 2 according to anotherembodiment of this invention [FIG. 11 does not show the pixel electrodes3]. This embodiment differs from the FIG. 1 embodiment in that acrosssubstantially the entire display viewing area on the active plate, thecolumns (or rows) of pixels between respective drain address lines 5extending in one axial direction are each of a single color. Forexample, as illustrated in FIGS. 6(a) and 11, column 111 of pixels onthe display area includes only red pixels with a single red color filterstrip 101, while column 112 of pixels includes only green pixels with asingle green filter strip 102, and column 113 includes only blue pixelswith a single blue filter strip 103. Therefore, red color filtermaterial 1 may be deposited and patterned on the active substrate into aplurality or array of elongated strips which correspond to the red pixelcolumns, thereby eliminating the need to pattern each red pixel filterindividually as a square. Therefore, because the materials 101-104 areonly patterned into elongated columns (or rows) extending in one axialdirection, gaps “P” exist over top of, and along the length of, one setof address lines, but not the other set which remains covered for themost part. The green and blue color filter materials 102-103 are alsopatterned into columns as illustrated.

As illustrated in FIGS. 6(a) and 11, gaps “P” between adjacent differentcolored filter materials are present along substantially the entirelengths of the column lines (drain lines 5), while gate address lines 7are for the most part covered up entirely with the insulating colorfilter materials, except for very small areas proximate the drain lines5 where the gap “P” exists between adjacent color filters.

Referring to FIG. 6(a), each pixel also includes the storage capacitorincluding contact hole 36 through which the corresponding pixelelectrode 3 contacts the upper molybdenum electrode 12 of the storagecapacitor. The bottom electrode of each storage capacitor is formed by agate line 7. FIG. 6(a) illustrates only three pixels, red, green, andblue, proximate one edge 121 of the viewing area. As will be appreciatedby those of skill in the art, hundreds, if not thousands, of differentcolored pixels extended across the entire viewing area, with eachmaterial 101-104 extending and being patterned into an array of stripsacross same. For example, red color filter 101 that is illustrated inFIG. 6(a) extends downwardly in direction 122 across the entire displayviewing area (see FIG. 11), as do filter strips 102 and 103. If whitepixels are present, clear layer 104 strips will also be included. Alsoillustrated in FIG. 6(a) at the bottom of each of the three pixels, arethe storage capacitors which correspond to the colored pixels belowthose illustrated.

Another difference between the FIGS. 6(a)-6(c) embodiment relative tothe FIG. 1 embodiment, is that in the FIGS. 6(a)-6(c) embodiment thegate electrode 17 of each TFT is formed as a perpendicular extensionwhich protrudes from a gate line 7. Meanwhile, the drain electrode 13 ofeach TFT is formed as a perpendicular extension which protrudes from theedge of a respective drain address line 5. Pixel electrodes 3 contactsource electrodes 15 through contact holes 35 which are illustrated inFIGS. 6(a) and 11 with “X” sectioning.

FIG. 6(b) is a side cross-sectional view of the active plate of FIG.6(a), taken along viewing line A—A with FIG. 6(b) also illustratingliquid crystal layer 45 and the common electrode 49 which is disposed onthe passive substrate 51.

FIG. 6(c) is a side cross-sectional view of the active plate of FIG.6(a), taken along viewing line B—B.

Referring to FIGS. 1-11, color filters 101-103, and clear layer 104,each have a dielectric constant less than or equal to about 5.0(preferably less than or equal to about 4.0, and even more preferablyless than or equal to about 3.0) according to certain embodiments ofthis invention, and are deposited and patterned on active substrate 19so as to at least partially cover the TFTs 9 and at least one of addresslines 5 and 7 in overlap areas. These low dielectric constant valueshave been found to reduce cross-talk and reduce line-pixel capacitancevalues, both of which are desirable results. For example, the red colorfilters 101 may be formed on substrate 19 by depositing red color filterlayer 101 and thereafter patterning same via known photolithographyand/or etching so as to form the-various red color filter strips orsquares 101 across the substrate in the red pixel areas. Thereafter thegreen color filter strips or squares 102 may be formed by depositing alayer of the green color filter material on substrate 19 and thereafterpatterning same via photo-imaging or the like so as to form the array ofgreen color filter strips or squares 102 on the substrate. The bluecolor filter strips or squares may be formed in a similar manner as maythe array of clear insulators 104.

Each color filter 101-103 may be formed of a color dye or pigmentinclusive photo-imageable material such as a filter material availablefrom Fuji [Olin Macroelectronics Materials, Rhode Island] known as ColorMosaic™, red, green, and blue, product Nos. CR-6200L, CG-6030L, andCB-6030L respectively. The refractive index of each color filter is, forexample, for the red color filter 1.60, for the green 1.52, and for theblue 1.83. Generally, the refractive index of each color filter 101-103is from about 1.50 to 2.00. The photo-imageable nature of the colorfilters 101-103, and clear layer 104, permits vias or contact holes 35to be formed therein and also simultaneously allows the color filters tobe patterned on the active substrate. Optionally, vias or contacts holes36 may also be simultaneously formed in the color filters so as to allowformation of the storage capacitors.

Each color filter 101-103 (and material 104) is of a material which hasa dielectric constant ∈ less than or equal to about 5.0 according tocertain embodiments of this invention [at room temperature and about 1kHz as known in the art]. In certain preferred embodiments, each colorfilter layer has a dielectric constant less than or equal to about 4.0(even more preferably less than or equal to about 3.0). In certainpreferred embodiments, the clear layer 104 has a dielectric constant ∈of about 2.7 and may be made of a transparent photo-imageable type ofBenzocyclobutene (BCB), for the purpose of reducing capacitivecross-talk (or capacitive coupling) between the pixel electrodes and theaddress lines in overlap areas 18. Alternatively, the layer 104 may bemade of Fuji Clear™. Each color filter has a relatively low dielectricconstant and/or a relatively high thickness for the specific purpose ofreducing C_(PL) in the overlap areas. Alternatively, otherphoto-imageable dye inclusive materials having such low dielectricconstants may be utilized for color filters 101-103.

Following the deposition and patterning of the color filters 101-103,and layer 104, on active plate 19 over top of the TFTs 9 and addresslines 5, 7, vias 35 are formed in the color filters 101-103, and layer104, by way of either photo-imaging, wet etching, or dry etching inother embodiments. The color filters and layer 104, in photo-imageableembodiments, act as negative working resist layers so that UV exposedareas remain on the substrate and areas unexposed to UV duringphoto-imaging are removed during developing. Optionally, vias or contactholes 36 may also be formed at this time. Following the forming of thevias or contact holes in the different patterned filters 101-103, andlayer 104, substantially transparent pixel electrodes 3 (e.g. made ofindium tin oxide or ITO) are deposited and patterned over the colorfilters 101-103 and layer 104 on the active plate so that each pixelelectrode 3 contacts the corresponding source metal layer 31 of thecorresponding TFT 9 through a via 35 as illustrated in FIGS. 4 and 6.

The thickness of each color filter 101-103 (and layer 104) may varyaccording to certain embodiments of this invention. For example, redcolor filters 101 may be thinner than green color filters 102 or viceversa, with blue 103 being thicker than both the red and green filters.In preferred embodiments, the thickness “d” of each color filter rangesfrom at least about 1.0 μm in overlap areas 18. In other embodiments,the thickness “d” of each color filter is from about 1.0 to 3.0 μm, andpreferably from about 1.5-2.5 μm. The thickness of all of the strips orlayers 101-104 may be substantially the same in certain embodiments.

Because of the low dielectric constant ∈ and/or relatively highthickness of each color filter 101-103 and layers 104, the capacitivecross-talk problems of the prior art resulting from overly high C_(PL)values are substantially reduced in overlap areas 18 where the pixelelectrodes 3 overlap the address lines and/or TFTs. Meanwhile, due tothe certain overlapping between address line(s) and color filters/pixelelectrodes, the possible liquid crystal disclinations at the pixel edgeswill be substantially overcome. Furthermore, the manufacturing of thesedisplays is improved (i.e. the total number and/or complexity of thesteps is reduced), as the number of total process steps on both activeand passive plates is reduced. Also, it is easier to align the opposingplates. Because the color filters are disposed between the pixelelectrodes and the address lines in the overlap areas 18, the capacitivecross-talk problems of the prior art are substantially reduced oreliminated, and increased pixel openings are achieved withoutsacrificing display performance (pixel isolation).

Pixel opening sizes or the pixel aperture ratio of AMLCD 2 is at leastabout 65% (preferably from about 68% to 80%) according to certainembodiments of this invention when the pixel pitch is a reference ofabout 150 μm. The pixel aperture ratio will, of course, vary dependingupon the pixel pitch of the display (pixel pitch is from about 40-500 μmmay be used). Pixel electrodes 3 overlap address lines 5 and/or 7 alongthe edges thereof as shown in FIG. 1 by an amount of up to about 3.0 μm.In certain preferred embodiments of this invention, the overlap 18 ofelectrodes 3 over the edges of the address lines is designed to be fromabout 2 to 3 μm, with the end result after over-etching being at leastabout 0.5 μm. According to certain other embodiments of this invention,the amount of overlap may be designed to be from about 2-3 μm, with theresulting post-processing overlap being from about 0.1 to 2.0 μm. Theoverlap amount between the address lines and pixel electrodes may beadjusted in accordance with different LCD applications and pixel pitchsizes as would be appreciated by those of skill in the art.

With regard to the overlap amount of the color filters 101-103, andlayer 104, over the address lines 5, 7, the color filters 101-103, andlayer 104, overlap the address lines to a greater degree than do thecorresponding pixel electrodes 3. For example, color filter 101 in thered pixel of FIG. 1 may overlap a corresponding address line (5 and/or7) by about 1.0 μm while the pixel electrode 3 of that pixel onlyoverlaps the same address line by about 0.5 μm. The patternedsubstantially co-planar arrays of filters 101-103 and layer 104 are allcharacterized by these traits.

In certain situations, after etching and processing, pixel electrodes 3may not overlap the address lines at all while the filters do stilloverlap the line(s) according to certain embodiments of this invention,although some overlap by both is preferred. When no overlap by the pixelelectrodes 3 occurs, the parasitic capacitance C_(PL) between theaddress lines and the adjacent pixel electrodes 3 is still minimized orreduced due to the insulating function of the color filters 101-103 andclear layer 104, which do overlap the address lines.

Referring now to FIGS. 1-11, it will be described how AMLCD 2 includingthe array of TFT structures and corresponding address lines is made ormanufactured according to one embodiment of this invention. First,substantially transparent active substrate 19 is provided. Next, a gatemetal layer or sheet (which results in gate electrodes 17) is depositedon the top surface (the surface which faces the liquid crystal layer) ofsubstrate 19 to a thickness of from about 1,000-5,000 Å, most preferablyto a thickness of about 2,500 Å. The gate metal sheet is deposited byway of sputtering or vapor deposition. The gate metal may be of tantalum(Ta) according to certain embodiments of this invention. Insulatingsubstrate 19 may be of glass, quartz, sapphire, or the like.

The structure including active substrate 19 and the deposited gate metalis then patterned by photolithography to the desired gate electrode 17and gate address line 7 configuration. The upper surface of the gatemetal is exposed in a window where the photoresist has not beenretained.

The gate metal (e.g. Ta) layer is then dry etched (preferably usingreactive ion etching or RIE) in order to pattern the gate metal layer inaccordance with the retained photoresist pattern. To do this, thestructure is mounted in a known RIE apparatus which is then purged andevacuated in accordance with known RIE procedures and etchants. Thisetching of the gate metal layer is preferably carried out until the gatemetal is removed in center areas of the window and is then permitted toproceed for an additional time (e.g. 20 to 40 seconds) of overetching toensure that the gate metal is entirely removed from within the windows.The result is the gate address lines 7 (and gate electrodes 17) beingleft on active substrate 19. In the FIG. 6 embodiment, the gateelectrode 17 are formed as extensions which protrude from the gate lines7, while in FIGS. 1 and 4 the gate electrodes are part of the actualgate lines 7.

After address lines 7 and electrode 17 are deposited and patterned ontop of substrate 19, gate insulating or dielectric layer 21 is depositedover substantially the entire substrate 19 preferably by plasma enhancedchemical vapor deposition (CVD) or some other process known to produce ahigh integrity dielectric. The resulting structure is shown in FIG. 7.Gate insulating layer 21 preferably includes silicon nitride but mayalso include silicon dioxide or other known dielectrics. Silicon nitridehas a dielectric constant of about 6.4. Gate insulating layer 21 isdeposited to a thickness of from about 2,000-3,000 Å (preferably eitherabout 2,000 Å or 3,000 Å) according to certain embodiments.

It is noted that after anodization (which is optional), gate Ta layer 17which was deposited as the gate electrode 17 and gate line 7 layer (whenoriginally about 2,500 Å thick) is about 1,800 Å thick and a newlycreated Ta₂O₅ layer is about 1,600 Å. Anodization takes place after thegate line patterning and before further processing. Thus, gateinsulating layer 21 over gate lines 7 and electrodes 17 is made up ofboth the anodization created Ta₂O₅ layer and the silicon nitride layer.Other metals from which gate electrode 17 and address lines 7 may bemade include Cr, Al, titanium, tungsten, copper, and combinationsthereof.

After gate insulating layer 21 has been deposited, semiconductor (e.g.intrinsic a-Si) layer 23 is deposited on top of gate insulating layer 21to a thickness of about 2,000 Å (see FIG. 8). Semiconductor 23 may befrom about 1,000 Å to 4,000 Å thick in certain embodiments of thisinvention. Then, doped (typically phosphorous doped, that is n+)amorphous silicon contact layer 25 is deposited over intrinsic a-Silayer 23 in a known manner as shown in FIG. 8 to a thickness of, forexample, about 500 Å. Doped contact layer 25 may be from about 200Å-1,000 Å thick according to certain embodiments of this invention.

Gate insulating layer 21, semiconductor layer 23 and semiconductorcontact layer 25 may all be deposited on substrate 19 in the samedeposition chamber without breaking the vacuum in certain embodiments.When this is done, the plasma discharge in the chamber is stopped afterthe completion of the deposition of a particular layer (e.g. insulatinglayer 21) until the proper gas composition for deposition of the nextlayer (e.g. semiconductor layer 23) is established. Subsequently, theplasma discharge is re-established to deposit the next layer.Alternatively, layers 21, 23, and 25 may be deposited in differentchambers by any known method.

Following the formation of the FIG. 8 structure, the TFT island or areamay be formed by way of etching, for example, so that the TFT metallayers can be deposited thereon. Optionally, one of the TFT metalsource/drain layers may be deposited before forming the island.

According to certain embodiments, following the formation of the TFTisland from the FIG. 8 structure, a source-drain metal sheet or layer(which results in drain metal layer 29 and source layer 31) is depositedon substrate 19 over top of semiconductor layer 23 and contact layer 25.The result is TFT structure 9 with channel 27 (after patterning) isshown in FIG. 9.

Red color filter insulating layer 101 is then deposited ontosubstantially the entire substrate 19 by way of spin coating or printingaccording to certain embodiments of this invention. Layer 101 may be,for example, of red pigment or red dye inclusive photo-imageablematerial in certain embodiments. Layer 101 fills recesses generated uponformation of TFTs 9 and flattens the surface above substrate 19 at leastabout 60% according to certain embodiments.

The photo-imageable color filter layer 101 acts as a negative resistlayer according to certain embodiments of this invention so that noadditional photoresist is needed to pattern the layer 101 into the arrayof red color filters 101 and to form vias 35 and/or 36 in the layer. Inorder to pattern layer 101 and form vias 35 and/or 36, the layer isirradiated by ultraviolet (UV) rays (e.g. I-line of 365 nm), with UVirradiated areas of layer 101 remaining on the substrate and non-exposedor non-radiated areas of the layer being removed during developing. Amask may optionally be used. Thus, the areas of the negative resist 101corresponding to the vias and areas to be removed are not exposed to theUV radiation, while the rest of the layer which will result in the colorfilters is exposed to UV.

Following exposure of layer 101, the layer is developed by using a knowndeveloping solution at a known concentration. In the developing stage,the areas of layer 101 corresponding to vias 35 and/or 36 and theremainder of the active area where the filter is not to be present areremoved (i.e. dissolved) so as to pattern the red color filters 101 onthe active substrate and form vias 35 and/or 36 in same. Afterdeveloping, the resist layer 101 is cured or subjected to post-baking(e.g. about 240° C. for about one hour) to eliminate the solvent so thatthe layer therein is resinified. Thus, no dry or wet etching is neededto form the vias and pattern layer 101 into the plurality of colorfilters 101 which take the form of strips in the FIG. 6 embodiment, andthe form of squares in the FIG. 1 embodiment. According to alternativeembodiments, layer 101 may be a positive resist as opposed to a negativeresist in photo-imageable embodiments. Alternatively, the color filterlayers may be non-photo-imageable in some embodiments.

Vias or contact holes 35 are thus formed in insulation color filters 101over top of, or adjacent, each source metal electrode 31 so as to permitthe corresponding pixel electrodes 3 to electrically contactcorresponding source electrodes 15 through vias 35 in the red colorfilters 101. The color filters remains across the entire area of eachred pixel and each overlaps at least one of the adjacent address linesas shown in FIG. 1.

After the red color layer 101 is formed and patterned on activesubstrate 19 as discussed above, the green and blue color filter layers102 and 103, respectively, are formed on the substrate 19 and patternedin the same manner so as to form the arrays of green and blue colorfilters 102 and 103 in the green and blue pixel areas of the AMLCD. Thegreen and blue color filters 102 and 103 are formed and provided on thesubstrate in a manner similar to the red color filters 101 discussedabove. Other clear strips 104 may be formed and patterned on substrate19 in a similar manner if white pixels are desired. Optionally, the redcolor filters do not have to be formed first. For example, the colorfilters could be formed in the following order: green, blue, and red; orblue, green, and red. Any order may suffice.

After all color filters are formed and patterned on substrate 19, asubstantially transparent conducting layer (e.g. ITO) which results inpixel electrodes 3 is deposited and patterned (e.g. photo-masked andetched) on substrate 19 over top of the color filters. After patterning(e.g. mask and etching) of this substantially transparent conductinglayer, pixel electrodes 3 are left as shown in FIGS. 1, 3, 4, 5, and 6.As a result of the vias or contact holes 35 formed in the color filters,each pixel electrode 3 contacts a corresponding TFT source electrode 31.When contact holes 36 are provided, each pixel electrode 3 contacts astorage capacitor electrode 12. The result is the active plate of FIGS.1, 4, and 6, including an array of TFTs. The pixel electrode layer, whenmade of ITO, is deposited to a thickness of from about 300 Å to 900 Å(preferably about 600 Å) according to certain embodiments of thisinvention. Other known materials may be used as pixel electrode layer 3.

The instant inventors have found surprisingly that the thickness of themetal pixel electrode layer (and pixel electrodes 3) should be fromabout 300 Å-900 Å in this invention, because of the need to reduce theinterface stress between the pixel electrodes (e.g. ITO) and materials101-104.

After formation of the active plate, liquid crystal layer 45 is disposedand sealed between the active plate and the passive plate as shown inFIG. 5. The passive plate includes substrate 51, polarizer 53, commonelectrode 49, and orientation film 47. Meanwhile, the active plateincludes thereon polarizer 41, orientation film 43, and the structureillustrated in FIGS. 1, 4, and 6 (noting that FIGS. 4 and 6 aredifferent embodiments).

As shown in FIGS. 1, 6(a), 6(b), and 6(c), the pixel electrodes 3 andthe color filters 101-103 (and layer 104) are patterned to a size sothat they overlap both drain address lines 5 and gate address lines 7along the edges thereof so as to result in an increased pixel apertureratio for AMLCD 2. The cross-talk problems of the prior art aresubstantially eliminated due to the presence of the color filters inoverlap areas 18 between the pixel electrodes and address lines.Alternatively, the pixel electrodes need only overlap one group ofaddress lines (e.g. column lines) according to certain embodiments.

FIG. 5 is a side cross-sectional view of AMLCD 2 (of FIG. 1 or of FIG.6), absent the TFTs, color filters, address lines, etc. As shown, thetwisted nematic display includes from the rear forward toward theviewer, rear polarizer 41, substantially transparent active substrate19, pixel electrodes 3, rear orientation film 43, twisted nematic liquidcrystal layer 45, front orientation film 47, common electrode 49, frontsubstantially transparent substrate (passive substrate) 51, and finallyfront polarizer 53. Optionally, patterned black matrix/anti-refractivelayer may be inserted between substrate 51 and common electrode 49 inorder to reduce the possible refraction and/or reflection from theuncovered address lines, and shield TFTs from ambient light.Alternatively, a black matrix may be provided on address lines and TFTsbefore deposition of any polymer material is provided (i.e. on theactive plate). Polarizers 41 and 53 may-be arranged so that theirtransmission axes are either parallel or perpendicular to each other soas to define a normally black or normally white colored AMLCDrespectively. Optionally, retarders may also be provided between 19 andpolarizer 41 and/or 51 and polarizer 53.

Typically, a backlight is provided rearward of polarizer 41 so thatlight emitted therefrom first goes through polarizer 41, then through LClayer 45, and out of polarizer 53 toward the viewer. Pixel electrodes 3selectively work in conjunction with common electrode 49 so as toselectively apply voltage across LC layer 45 in different pixels so asto cause an image to be viewed from the front of the display.

Exemplary line pixel capacitance values according to this inventionrange from about 4.5 to 10.0 fF when the overlap distance is from about1-2 μm. Compare these values with a conventional coplanar LCD in whichthe pixel electrodes are substantially coplanar with the address linesand spaced therefrom, such a conventional LCD having a line pixelcapacitance of about 11.8 fF when the electrodes are spaced laterallyfrom the address lines by about 5 μm, and about 9.6 fF when the lateralspacing is about 10 μm. Thus the high aperture LCDs discussed hereinhave higher pixel aperture ratios than conventional LCDs withoutsuffering from substantially higher line pixel capacitance values. Thecapacitance values herein takes into consideration the fringingcapacitance in a known manner.

The line pixel capacitance is less than about 20 fF, preferably lessthan or equal to about 12 fF, and most preferably less than or equal toabout 7.0 fF according to this invention with the overlapped areas andhigh pixel apertures.

The line-pixel capacitance values (and insulating materials) of thisinvention are similar to those disclosed in Chart 1 of U.S. Pat. No.5,641,974, the disclosure of which is incorporated herein by reference.

The color filters disclosed herein have transmission characteristics sothat the pixels and LCD having viewing characteristics (e.g. contrastratios and inversion characteristics) as described in U.S. Pat. Nos.5,594,568 and 5,570,214 when the retarder configurations claimed thereinare used, the disclosures of which are hereby incorporated herein byreference.

Once given the above disclosure, many other features, modifications, andimprovements will become apparent to the skilled artisan. Such otherfeatures, modifications, and improvements are, therefore, considered tobe a part of this invention, the scope of which is to be determined bythe following claims.

We claim:
 1. A display including color filters, the display comprising:first and second substrates; first and second colored pixels, said firstpixel including a first pixel electrode, a first insulating colorfilter, and a first switching element, and said second pixel including asecond pixel electrode, a second insulating color filter, and a secondswitching element, wherein said first and second color filters aredifferently colored; said first pixel electrode overlapping at least oneaddress line in communication with said first switching element, andsaid second pixel electrode overlapping at least one address line incommunication with said second switching element, so as to define a highaperture display, said overlapping by said first and second pixelelectrodes forming areas of overlap; said first color filter being atleast partially disposed in an area of overlap formed by said firstpixel electrode and said first color filter having a dielectric constantof less than about 5.0 and a first contact hole defined therein thatallows said first pixel electrode to be in electrical communication withsaid first switching element; and said second color filter being atleast partially disposed in an area of overlap formed by said secondpixel electrode, and said second color filter having an dielectricconstant of less than about 5.0 and a contact hole defined therein thatallows said second pixel electrode to be in electrical communicationwith said second switching element.
 2. The display of claim 1, whereineach of said first and second color filters comprises photo-imageablematerial.
 3. The display of claim 2, wherein each of said first andsecond color filters comprises a negative resist.
 4. The display ofclaim 1, wherein each of said first and second color filters has arefractive index of from about 1.5 to 2.0.
 5. The display of claim 1,wherein each of said first and second color filters has a thickness offrom about 1.5-2.5 μm, and wherein the pixel aperture ratio of thedisplay is at least about 68%.